Passivation layer for ceramic based charge plates

Abstract: A charge plate structure for use in a continuous ink jet printer is provided with a protective layer of adhesively bonded polyimide film. The charge plate is fabricated by forming a substrate having charging electrodes along one edge and corresponding conductive leads on one surface. The surface of the charge plate is precleaned and the polyimide film is laminated thereto by means of heat and pressure. The resulting charge plate exhibits improved adhesion and protection from ink.

Description: Technical Field The present invention relates to continuous ink jet printers and, more particularly, to improved constructions for the charge plate structure in such printers. Background Art In continuous ink jet printing, electrically conductive ink is supplied under pressure to a manifold region that distributes the ink to a plurality of orifices, typically arranged in a linear array(s). The ink discharges from the orifices in filaments which break into droplet streams. Individual droplet streams are selectively charged in the region of the break off from the filaments and charge drops are deflected from their normal trajectories. The deflected drops may be caught and recirculated, and the undeflected drops allowed to proceed to a print receiving medium. Drops are charged by a charge plate having a plurality of charging electrodes along one edge, and a corresponding plurality of connecting leads along one surface. The edge of the charge plate having the charging electrodes is placed in close proximity to the break off point of the ink jet filaments, and charges applied to the leads to induce charges in the drops as they break off from the filaments. U.S. Patent No. 4,560,991, issued December 24, 1985, to W. Shutrum, describes one method of fabricating a charge plate for an ink jet printer. The charge plate taught by Shutrum is fabricated by electro-depositing the charging electrodes and leads on a flat sheet of etchable material, such as copper foil, to form a so-called "coupon." The coupon is bent in a jig at approximately a 90°angle. The leads are then bonded to a charge plate substrate, and the etchable material is removed. In the prior art, charge plates are presently coated with multiple wet layers, such as a photoresist available as KTFR Photoresist from Union Carbide Corporation, lacquers, and epoxies. Such coatings provide insufficient protection of the charge leads as compared to a solid layer of polyimide. Wet coatings are prone to pinholing, and marginal adhesion, are not easily controllable and have erratic results. Coatings applied by wet methods inherently form an uneven interface at the leading edge of the coating on the charge plate surface where the conductors form a 90° angle. One method for solving this problem is disclosed in commonly assigned pending application U.S. Serial No. 857,852, which teaches coating the conductive lead surface of a charge plate with a two-part epoxy. Although epoxy such as EPO-TEK 353ND from Epoxy Technologies, Billerica, Massachusetts, is shown to be resistent to some ink jet inks, the two-part curable epoxy can be inconvenient to apply. Summary of the Invention It is therefore the object of the present invention to provide a charge plate having a polyimide dry film lamination that avoids the problems noted above. A solid layer of polyimide is convenient to apply, assures good adhesion, and eliminates pinholes. Polyimide sheet can be preformed to establish the desired interface with the charge plate surface. The setback distance and coating angle on the top charge plate surface can be control led by cutting the polyimide sheet to the exact size and shape required. A charge plate according to the present invention is provided with a polyimide dry film lamination which provides improved adhesion and impervious protection from ink. The invention provides a method of making a charge plate for use in an ink jet printer, comprising the steps of forming a charge plate having a plurality of charging electrodes along an edge of a ceramic substrate and a corresponding plurality of conductive leads on a surface of said substrate, precleaning the surface to ensure complete wettability; and laminating a polyimide dry film layer by heating and applying pressure. The invention further provides a charge plate for use in an ink jet printer as claimed in claim 3 below. The invention will now be described in more detail and by way of example only, with reference to the accompanying drawings, in which: Fig. 1 is a schematic partial cross-sectional view of a charge plate according to the present invention; and Fig. 2 is a flow chart illustrating the steps employed to fabricate the charge plate of Fig.1 Referring to the drawings, fig 1 illustrates a partial schematic cross-sectional diagram of a charge plate fabricated according to the present invention. It will be understood that such charge plate generally denoted 10 cooperates with other known components used in continuous ink jet printers. That is, the charge plate 10 functions with a drop generator, drop catcher (which may be integral with the charge plate), media feed station, and data handling and machine control electronics (not shown) to selectively charge the drops to effect ink jet printing. The charge plate 10 includes an insulating substrate 12 on which are formed conductive leads 14 and drop charging electrodes 16. The conductive leads 14 and drop charging electrodes 16 are covered by a protective layer 18 of adhesively bonded polyimide film. The laminating is preferably by means of heat and pressure. Referring now to Fig. 2, the charge plate shown in Fig. 1 is fabricated in the following manner. First, the charge plate is formed (20) with the leads and charging electrodes preferably as shown in U.S. Patent 4,560,991. Next, the charge plate is precleaned (22) to insure complete wettability of the top surface bearing the conductive leads 14, thereby assuring that the lamination to follow covers all conductive leads. The top of the charge plate is next laminated with a protective layer of adhesively bonded polyimide film (24). Finally, the polyimide film is bonded to the charge plate (26) by applying sufficient heat and pressure. In a preferred embodiment, the polyimide is bonded to the charge plate by applying approximately 250 pounds per square inch of pressure at approximately 350°F for approximately fifteen minutes, and then cooling the polyimide film to 250°F while maintaining pressure. The protective layer of adhesively bonded polyimide film can be applied using known techniques for laminating. For example, the bonding can be applied in a hydraulic press having electrically heated platens, or in a hot roll continuous laminator. A preferred grade of adhesively bonded polyimide is R/flex R 2000 (a registered trademark of Rogers Corp, Chandler, Arizona) coverfilm, one to three mils thick, having one mil of acrylic B-staged adhesive. Although B-staged adhesives are readily available and easy to apply, it is understood that other means of bonding a polyimide film to metals are equally applicable in the practice of this invention. Industrial Applicability and Advantages The present invention is useful in the field of ink jet printing, and has the advantage of providing improved protection of metallic charging leads from electrical short circuits. The present invention provides the further advantage of giving the charge plate circuitry impervious protection from ink. The polyimide film coating according to the present invention is compatible with the ink jet printing ink formulations available from Eastman Kodak Company. The preferred lamination means provides easily controllable, high uniform coverage, and the precleaning process insures complete coverage of the polyimide film coating. Having described the invention in detail and by reference to the preferred embodiment thereof, it will be apparent that other modifications and variations are possible without departing from the scope of the invention defined in the appended claims.

Claims: A method of making a charge plate for use in an ink jet printer, comprising the steps of: forming a charge plate (10) having a plurality of charging electrodes (16) along an edge of a ceramic substrate (12) and a corresponding plurality of conductive leads (14) on a surface of said substrate, precleaning the surface to ensure complete wettability; and laminating a polyimide dry film (18) layer by heating and applying pressure. A method as claimed in claim 1, wherein the steps of heating and applying pressure comprise: applying approximately 1.7 MPa (250 pounds/sq.inch) of pressure at approximately 177 °C (350 °F) for approximately fifteen minutes; and cooling the polyimide film to 121 °C (250 °F) while maintaining the pressure. A charge plate for use in an ink jet printer comprising: an electrically insulating ceramic charge plate substrate (12); a plurality of charging electrodes (16) disposed along an edge of said charge plate substrate and a corresponding plurality of electrical leads (14) disposed on a surface of said charge plate substrate; and an adhesively bonded polyimide dry film (18) layer. A charge plate as claimed in claim 4 or 5, wherein said charging electrodes (16) are nickel.

Inventors: SEXTON RICHARD W, SEXTON, RICHARD W.
Applicants: SCITEX DIGITAL PRINTING INC, SCITEX DIGITAL PRINTING, INC.
Application year: 1994
Main classification: B41J2
IPC codes: B41J2